JP2022186298A - Aqueous coating composition and method for manufacturing coated article - Google Patents

Abstract

To provide an aqueous coating composition which gives a coating film excellent in water resistance.SOLUTION: The aqueous coating composition contains: a main agent (A) containing a hydroxyl group-containing resin (a1) and an aqueous solvent (a2); and a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group. At least one of the main agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups. The content of the silane coupling agent is, for example, 1 pt.mass or more and 10 pts.mass or less based on 100 pts.mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1).SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a method for producing an aqueous coating composition and coated articles.

Conventionally, solvent-based paints have been used to paint automobiles because they tend to improve sharpness and finished appearance.
In recent years, interest in the environment has increased, and the demand for water-based paints has increased in place of solvent-based paints. (For example, Patent Document 1)

Japanese Patent Application Laid-Open No. 2020-22948

However, coating films formed from water-based paints generally have poor water resistance.
An object of the present invention is to provide a water-based coating composition that provides a coating film with excellent water resistance. Another object of the present invention is to provide a method for producing a coated article having a coating film formed from the above coating composition.

The present invention provides the following aspects [1] to [8].
[1]
a main agent (A) containing a hydroxyl-containing resin (a1) and an aqueous solvent (a2);
and a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group,
At least one of the main agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups.

[2]
[ 1].

[3]
A water-based coating composition used as a primer surfacer,
[ 1].

[4]
An aqueous coating composition for forming a clear coating film,
The content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1). The aqueous coating composition according to [1] above.

[5]
A step (I) of applying a water-based primer surfacer (X) to an object to be coated to form a base coating film;
A step (II) of applying an aqueous colored base coating composition (Y) onto the undercoating film to form a colored base coating film;
A step (III) of coating the aqueous clear coating composition (Z) on the colored base coating to form a clear coating,
At least one of the water-based primer surfacer (X) and the water-based clear coating composition (Z) contains a silane coupling agent having one or more epoxy groups.

[6]
The aqueous primer surfacer (X) comprises a first main agent (A1) containing a first hydroxyl group-containing resin (a11) and a first aqueous solvent (a21);
and a first curing agent (B1) containing a first polyisocyanate compound (b11) and a first organic solvent (b21) having no hydroxyl group,
The silane coupling agent is contained in at least one of the first main agent (A1) and the first curing agent (B1),
The content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the total solid content of the first hydroxyl-containing resin (a11) and the first polyisocyanate compound (b11). A method for producing a coated article according to [5] above.

[7]
The aqueous clear coating composition (Z) comprises a second main agent (A2) containing a second hydroxyl group-containing resin (a12) and a second aqueous solvent (a22),
and a second curing agent (B2) containing a second polyisocyanate compound (b12) and a second organic solvent (b22) having no hydroxyl group,
The silane coupling agent is contained in at least one of the second main agent (A2) and the second curing agent (B2),
The content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass with respect to 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12). A method for producing a coated article according to [5] above, which is as follows.

[8]
The method for producing a coated article according to any one of [5] to [7] above, wherein both the water-based primer surfacer (X) and the water-based clear coating composition (Z) contain the silane coupling agent.

ADVANTAGE OF THE INVENTION According to this invention, the water-based coating composition from which a coating film excellent in water resistance is obtained is provided. According to the present invention, there is also provided a method for producing a coated article having a coating film formed from the aqueous coating composition.

The water-based coating composition according to this embodiment is a two-pack type containing a main agent (A) and a curing agent (B). The main agent (A) contains a hydroxyl group-containing resin (a1) and an aqueous solvent (a2). The curing agent (B) contains a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group. At least one of the main agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups (hereinafter referred to as an epoxy group-containing silane coupling agent).

When the main agent (A) and the curing agent (B) are mixed, the hydroxyl group-containing resin (a1) contained in the main agent (A) is crosslinked by the polyisocyanate compound (b1) to obtain a cured coating film. At this time, the epoxy group-containing silane coupling agent also reacts with at least one of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1) to form a crosslinked structure. This increases the crosslink density of the cured coating film. As a result, water resistance is improved.

[Aqueous paint composition]
The water-based coating composition according to the present embodiment includes, for example, a coating for forming a base coating (so-called water-based primer surfacer), a coating for forming a colored base coating (colored base coating composition), and a coating for forming a clear coating. It is used as a paint (aqueous clear paint composition). When forming a multilayer coating film, the water resistance of the entire multilayer coating film is improved by using the water-based coating composition according to the present embodiment as a coating material for forming at least one layer.

The silane coupling agent also improves the adhesion between the cured coating film and the object to which it is applied. Therefore, the water-based coating composition is particularly suitable as a water-based primer surfacer for automobiles. This is because the primer surfacer is applied directly to the object to be coated. The aqueous coating compositions are also suitable for forming various coatings for repairing automotive coatings. This is because the coating film for repair is required to have high adhesion to the existing coating film in addition to the object to be coated.

In order to further improve water resistance, when forming a multilayer coating film, a water-based primer surfacer containing an epoxy group-containing silane coupling agent and a water-based clear coating composition containing an epoxy group-containing silane coupling agent are used in combination. preferably.

Hereinafter, the water-based coating composition for forming a base coating film is referred to as water-based primer surfacer (X). The main agent (A) contained in the water-based primer surfacer (X) is called the first main agent (A1), and the curing agent (B) is called the first curing agent (B1). The hydroxyl group-containing resin (a1) contained in the first main agent (A1) is called the first hydroxyl group-containing resin (a11), and the aqueous solvent (a2) is called the first aqueous solvent (a21). The polyisocyanate compound (b1) contained in the first curing agent (B1) is called the first polyisocyanate compound (b11), and the organic solvent (b2) is called the first organic solvent (b21).

Hereinafter, the aqueous coating composition for forming a clear coating film is referred to as an aqueous clear coating composition (Z). The main agent (A) contained in the aqueous clear coating composition (Z) is called the second main agent (A2), and the curing agent (B) is called the second curing agent (B2). The hydroxyl group-containing resin (a1) contained in the second main agent (A2) is called the second hydroxyl group-containing resin (a12), and the aqueous solvent (a2) is called the second aqueous solvent (a22). The polyisocyanate compound (b1) contained in the second curing agent (B2) is called a second polyisocyanate compound (b12), and the organic solvent (b2) is called a second organic solvent (b22).

Hereinafter, the first main agent (A1) and the second main agent (A2) are collectively referred to as main agent (A). The first curing agent (B1) and the second curing agent (B2) are collectively referred to as curing agent (B). The first hydroxyl-containing resin (a11) and the second hydroxyl-containing resin (a12) are collectively referred to as hydroxyl-containing resin (a1). The first aqueous solvent (a21) and the second aqueous solvent (a22) are collectively referred to as the aqueous solvent (a2). The first polyisocyanate compound (b11) and the second polyisocyanate compound (b12) are collectively referred to as polyisocyanate compound (b1). The first organic solvent (b21) and the second organic solvent (b22) are collectively referred to as organic solvent (b2).

Aqueous coating compositions are prepared using methods commonly used by those skilled in the art. The water-based paint composition is prepared by mixing each component by, for example, a kneading mixing method using a kneader or rolls or a dispersing mixing method using a sand grind mill or disper.

<Epoxy Group-Containing Silane Coupling Agent>
Silane coupling agents typically have both reactive silyl groups and organic functional groups. The epoxy group-containing silane coupling agent has one or more epoxy groups as organic functional groups. The epoxy group-containing silane coupling agent may have two or more epoxy groups.

An epoxy group is a three-membered ring (oxirane ring) having an ether bond. The epoxy group has high reactivity and reacts with the hydroxyl group-containing resin (a1) and/or the polyisocyanate compound (b1). Therefore, the crosslink density of the resulting cured coating film is increased.

An epoxy group is represented, for example, by the following structural formula (1).

Epoxy groups may be cycloaliphatic. The alicyclic epoxy group includes, for example, an epoxycyclohexyl group represented by the following structural formula (2).

The epoxy group-containing silane coupling agent may have other organic functional groups. However, when the epoxy group-containing silane coupling agent is contained in the main agent (A), it is desirable that the isocyanate group is not contained as an organic functional group. This is because if the hydroxyl group-containing resin (a1) and the epoxy group-containing silane coupling agent react with each other before the main agent (A) and the curing agent (B) are mixed, the crosslink density of the cured coating film is unlikely to increase. be. When the epoxy group-containing silane coupling agent is contained in the curing agent (B), the organic functional groups include hydroxyl groups and amino groups (primary, secondary and tertiary amino groups, and amino groups to which epoxy groups are bonded). should not be included. This is because if the polyisocyanate compound (b1) and the epoxy group-containing silane coupling agent react with each other before the main agent (A) and the curing agent (B) are mixed, the crosslink density of the cured coating film is unlikely to increase. be. Other desirable organic functional groups include, for example, acrylamide, acryloyl, methacryloyl, allyl, vinyl, styryl and mercapto groups.

The reactive silyl group is not particularly limited as long as it produces a silanol group by hydrolysis. Examples of reactive silyl groups include trialkoxysilyl groups (the number of carbon atoms contained in the alkoxy group is preferably 1 to 7), dialkoxyalkylsilyl groups (the number of carbon atoms contained in the alkoxy group is preferably 1 to 7, alkyl The number of carbon atoms contained in the group is preferably 1 to 7), more specifically, trimethoxysilyl group, triethoxysilyl group, tripropoxysilyl group, tris(2-methoxyethoxy)silyl group, dimethoxyalkyl silyl group, diethoxyalkylsilyl group, dipropoxyalkylsilyl group, bis(2-methoxyethoxy)alkylsilyl group (the above alkyl group may be a linear or branched alkyl group having 1 to 7 carbon atoms ). The multiple reactive silyl groups may be the same or different. Among them, a trialkoxysilyl group is preferable, a trialkoxysilyl group having 1 to 3 carbon atoms contained in the alkoxy group is more preferable, and a triethoxysilyl group is particularly preferable, because the water resistance can be more easily improved.

The epoxy group-containing silane coupling agent is contained in at least one of the main agent (A) and curing agent (B). Among them, the epoxy group-containing silane coupling agent is preferably contained in the curing agent (B) in terms of excellent miscibility with the polyisocyanate compound (b1).

The content of the epoxy group-containing silane coupling agent is preferably 1 part by mass or more, and 1.1 parts by mass or more with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1). is more preferable, and 1.2 parts by mass or more is particularly preferable. When the content of the epoxy group-containing silane coupling agent is within this range, the water resistance is more easily improved. The content of the epoxy group-containing silane coupling agent is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, relative to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1). Preferably, 6 parts by mass or less is particularly preferable. When the content of the epoxy group-containing silane coupling agent is within this range, the storage stability of the agent containing the epoxy group-containing silane coupling agent is likely to be improved.

When the aqueous coating composition is the aqueous primer surfacer (X), the content of the epoxy group-containing silane coupling agent is 100 of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11). It is preferably 1 part by mass or more, more preferably 1.1 parts by mass or more, and particularly preferably 1.2 parts by mass or more. The content of the epoxy group-containing silane coupling agent is preferably 8 parts by mass or less, and 6 parts by mass with respect to 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11). Parts or less is more preferable, and 5 parts by mass or less is particularly preferable.

When the water-based coating composition is the water-based clear coating composition (Z), the content of the epoxy group-containing silane coupling agent is the total solids of the second hydroxyl-containing resin (a12) and the second polyisocyanate compound (b12). It is preferably 1.2 parts by mass or more, more preferably 1.3 parts by mass or more, and particularly preferably 2 parts by mass or more per 100 parts by mass. The content of the epoxy group-containing silane coupling agent is preferably 10 parts by mass or less, and 8 parts by mass with respect to 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12). Parts or less is more preferable, and 6 parts by mass or less is particularly preferable.

The aqueous coating composition may contain silane coupling agents other than the epoxy group-containing silane coupling agent. However, from the viewpoint of water resistance, the ratio of the epoxy group-containing silane coupling agent to the total silane coupling agent is preferably 80% by mass or more, preferably 90% by mass or more. As described above, other silane coupling agents contained in the main agent (A) desirably do not have isocyanate groups. Other silane coupling agents contained in the curing agent (B) desirably do not have hydroxyl groups and amino groups (including primary, secondary and tertiary amino groups, and epoxy group-bonded amino groups).

<Main agent (A)>
The main agent (A) contains a hydroxyl group-containing resin (a1) and an aqueous solvent (a2). The solid content of the main agent (A) is not particularly limited. The solid content concentration of the main agent (A) is, for example, 30% by mass or more and 60% by mass or less.

(Hydroxyl group-containing resin (a1))
The hydroxyl group-containing resin (a1) is in the form of an emulsion dispersed in the aqueous solvent (a2). The particle size of the hydroxyl group-containing resin (a1) in the main agent (A) is not particularly limited. The average particle size of the hydroxyl group-containing resin (a1) is preferably 0.01 μm or more and 1.0 μm or less, and is preferably 0.05 μm or more and 0.5 μm or less, in terms of ease of viscosity control and appearance of the resulting coating film. more preferred. The average particle size is the 50% size (median size, D50) in the volume-based particle size distribution measured by the dynamic light scattering method.

The solid content concentration of the hydroxyl group-containing resin (a1) is, for example, 15 mass % or more and 95 mass % or less of the total solid content contained in the main agent (A). When the solid content concentration of the hydroxyl group-containing resin (a1) is within the above range, the strength of the resulting coating film tends to increase. The solid content concentration of the hydroxyl group-containing resin (a1) may be 20% by mass or more, or may be 25% by mass or more, based on the total solid content in the main agent (A). The solid content concentration of the hydroxyl group-containing resin (a1) may be 85% by mass or less, or may be 80% by mass or less, of the total solid content contained in the main agent (A).

The hydroxyl value of the hydroxyl-containing resin (a1) is preferably 5 mgKOH/g or more and 200 mgKOH/g or less, more preferably 50 mgKOH/g or more and 150 mgKOH/g or less. When the hydroxyl value of the hydroxyl-containing resin (a1) is within the above range, the strength of the resulting coating film is sufficiently high, and the water resistance is easily improved.

The acid value of the hydroxyl group-containing resin (a1) is not particularly limited, and may be, for example, 5 mgKOH/g or more and 100 mgKOH/g or less, or 10 mgKOH/g or more and 50 mgKOH/g or less. When the acid value of the hydroxyl-containing resin (a1) is within the above range, the water-dispersibility of the hydroxyl-containing resin (a1) increases, and the water resistance of the resulting coating film tends to improve.

The number average molecular weight of the hydroxyl group-containing resin (a1) is not particularly limited, and may be, for example, from 1,000 to 100,000, from 2,000 to 50,000, from 3,000 to 10, 000 or less. When the number average molecular weight of the hydroxyl group-containing resin (a1) is within the above range, an excessive increase in the viscosity of the water-based coating composition is suppressed, and the resulting coating film has an improved appearance and a sufficiently high strength. easy to become

Both hydroxyl value and acid value are based on solid content and can be measured according to JIS K 0070. A number average molecular weight is a styrene homopolymer conversion value measured using a gel permeation chromatography.

The hydroxyl group-containing resin (a1) is not particularly limited as long as it has one or more, preferably two or more hydroxyl groups. Examples of hydroxyl group-containing resins (a1) include acrylic polyols, polyester polyols, polyether polyols, polyurethane polyols, and polycarbonate polyols. Among them, acrylic polyols are preferable in that various physical properties such as the appearance, weather resistance, and chemical resistance of the coating film to be obtained are likely to be improved.

The hydroxyl group-containing resin (a1) is obtained, for example, by emulsion polymerization of one or more raw material monomers. Emulsion polymerization is carried out by a method commonly practiced by those skilled in the art. Specifically, an emulsifier is mixed with an aqueous medium containing an organic solvent such as alcohol as necessary, and the raw material monomers and the polymerization initiator are added dropwise while the resulting mixture is heated and stirred. Alternatively, an emulsified mixture obtained by previously emulsifying raw material monomers, an emulsifier and water may be dropped into an aqueous medium. The aqueous medium may be the same as or different from the aqueous solvent (a2).

Emulsions of acrylic polyols are produced by, for example, emulsion polymerization of a raw material monomer mixture containing (meth)acrylic acid alkyl ester monomers, acid group-containing ethylenically unsaturated monomers, hydroxyl group-containing ethylenically unsaturated monomers, and styrene monomers. can get.

(Aqueous solvent (a2))
Examples of aqueous solvents include various types of water such as pure water, ion-exchanged water, tap water, and industrial water. The main agent (A) may contain an organic solvent together with the aqueous solvent. Examples of organic solvents include diethylene glycol dibutyl ether (dibutyl diglycol), dipropylene glycol dimethyl ether, butyl acetate, ethyl diglycol acetate, propylene glycol methyl ether acetate, n-butyl alcohol, methoxypropanol, diethylene glycol monobutyl ether, ethylene glycol monobutyl ether. Butyl ether, toluene, xylene, methyl isobutyl ketone, methyl ethyl ketone.

(others)
The main agent (A) may contain a resin containing no hydroxyl group, if necessary. The main agent (A) may also contain various additives, if necessary, in addition to the hydroxyl group-containing resin (a1) and the aqueous solvent (a2). Additives include, for example, dispersants, defoamers, ultraviolet absorbers, hindered amine light stabilizers, antioxidants, viscosity modifiers, surface modifiers, coalescing agents, rust inhibitors and thickeners. . Among them, it is preferable to include a viscosity modifier and/or a surface modifier, since the appearance of the resulting coating film is likely to be further improved.

Viscosity modifiers include, for example, crosslinked resin particles (polymer compounds having a crosslinked structure in the molecule), inorganic viscosity agents, cellulose derivatives, and urethane association type viscosity agents. These are used singly or in combination of two or more. The amount of the viscosity modifier may be, for example, 0.1% by mass or more and 50% by mass or less, or 0.5% by mass or more and 30% by mass or less of the solid content of the hydroxyl group-containing resin (a1).

Examples of the surface control agent include silicone, acrylic, vinyl, and fluorine surface control agents. These are used singly or in combination of two or more. The amount of the surface conditioner may be, for example, 0.1% by mass or more and 10% by mass or less, or 0.2% by mass or more and 8% by mass or less of the solid content of the hydroxyl group-containing resin (a1).

(Method for preparing main agent (A))
The main agent (A) can be prepared by mixing the above components by methods known to those skilled in the art. Mixing methods include the same methods as those for preparing the water-based paint composition.

<Curing agent (B)>
The curing agent (B) contains a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group. The solid content of the curing agent (B) is not particularly limited. The solid content concentration of the curing agent (B) is, for example, 20% by mass or more and 70% by mass or less.

(Polyisocyanate compound (b1))
The polyisocyanate compound (b1) is not particularly limited as long as it has an average of two or more isocyanate groups per molecule. Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate, pentamethylene diisocyanate, tetramethylene diisocyanate and trimethylhexamethylene diisocyanate; Isocyanates; aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate; modified products thereof (e.g., urethane compounds, carbodiimides, uretdione, uretonimine, biuret forms, isocyanurates, etc.) .

The content of the polyisocyanate compound (b1) may be, for example, 20% by mass or more, or 30% by mass or more, of the total solid content of the curing agent (B).

(Organic solvent (b2))
The organic solvent (b2) is not particularly limited as long as it does not have a hydroxyl group. Examples of the organic solvent (b2) include ethylene glycol dimethyl ether (DMM), ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol divinyl ether, diethylene glycol ethyl methyl ether, diethylene glycol isopropyl methyl ether, diethylene glycol butyl methyl ether, and triethylene. Glycol dimethyl ether, triethylene glycol divinyl ether, tetraethylene glycol diethyl ether, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol di-n-propyl ether, propylene glycol diisopropyl ether, propylene glycol di-n-butyl ether, propylene glycol diisobutyl ether , propylene glycol diallyl ether, propylene glycol diphenyl ether, dipropylene glycol dimethyl ether (DPDM), dipropylene glycol diethyl ether, dipropylene glycol di-n-butyl ether, dipropylene glycol diisobutyl ether, dipropylene glycol diallyl ether, tripropylene glycol dimethyl ether, Tripropylene glycol diethyl ether, tripropylene glycol di-n-butyl ether, tripropylene glycol diisobutyl ether, tripropylene glycol diallyl ether, butylene glycol dimethyl ether, butylene glycol diethyl ether, butylene glycol di-n-butyl ether, 2-butoxyethyldiethoxy Glycol ether organic solvents such as ethyl ether, 2-butoxyethyltriethoxyether, 2-butoxyethyltetraethoxyethyl ether; ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol mono-n-butyl ether acetate, diethylene glycol Acetate-based organic solvents such as monoethyl ether acetate, diethylene glycol mono-n-butyl ether acetate, 3-methoxybutyl acetate, propylene glycol monomethyl ether acetate; ketone-based organic solvents such as acetone, methyl ethyl ketone, methyl amyl ketone, and methyl isobutyl ketone; acetic acid ethyl, ester organic solvents such as butyl acetate, isobutyl acetate, methyl benzoate, ethyl ethoxypropionate (EEP), ethyl propionate and methyl propionate; These are used singly or in combination of two or more.

(others)
The curing agent (B) may contain curing agents other than the polyisocyanate compound (b1). The content of other curing agents is, for example, 10% by mass or less of the total solid content of all curing agents.

(Method for preparing curing agent (B))
Curing agent (B) can be prepared by mixing the above components by methods known to those skilled in the art. Mixing methods include the same methods as those for preparing the water-based paint composition.

<Dilution component (C)>
A diluent component (C) may be further mixed with the aqueous coating composition. Examples of the diluent component (C) include the same as the aqueous solvent (a2). The diluent component (C) may be the same as or different from the aqueous solvent (a2).

The amount of the diluent component (C) to be mixed is appropriately set in consideration of the viscosity of the water-based coating composition, the coating method, and the like. The amount of the diluent component (C) mixed is, for example, 10 parts by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the solid content of the hydroxyl-containing resin (a1).

<Pigment (D)>
The aqueous primer surfacer (X) may further contain a pigment (D). The content of the pigment (D) is, for example, 100 parts by mass or more and 300 parts by mass or less, and 120 parts by mass or more with respect to 100 parts by mass of the resin solid content contained in the main agent (A1) of the aqueous primer surfacer (X). It may be 200 parts by mass or less.

Pigment (D) is not particularly limited. Examples of the pigment (D) include coloring pigments such as titanium dioxide, carbon black, iron oxide and copper phthalocyanine blue; luster pigments such as aluminum flakes and mica flakes; calcium carbonate, clay, talc, barium oxide, silica and the like. Extender pigments: rust preventive pigments such as aluminum tripolyphosphate, aluminum phosphomolybdate, and zinc phosphate;

Above all, it is preferable that at least an extender pigment is contained from the viewpoint of the abrasiveness and film-forming properties of the undercoating film. The proportion of the extender pigment is, for example, 30% by mass or more and 100% by mass or less, and may be 40% by mass or more and 70% by mass or less with respect to a total of 100 parts by mass of all pigments.

[Manufacturing method of coated article]
A coated article is prepared by applying a water-based primer surfacer (X) to an object to be coated to form a base coat (I), and coating a water-based colored base coating composition (Y) on the base coat. a step (II) of forming a colored base coating film; and a step (III) of coating the aqueous clear coating composition (Z) on the colored base coating film to form a clear coating film. Manufactured by

At least one of the water-based primer surfacer (X) and the water-based clear coating composition (Z) contains a silane coupling agent having one or more epoxy groups. This improves the water resistance of the entire multi-layer coating film. Above all, both the aqueous primer surfacer (X) and the aqueous clear coating composition (Z) preferably contain an epoxy group-containing silane coupling agent.

(I) Step of Forming Base Coat Film In this step, a water-based primer surfacer (X) is applied to the object to be coated to form a base coat film.

(Method for preparing aqueous primer surfacer (X))
The first hydroxyl group-containing resin (a11) and the first aqueous solvent (a21) are mixed to prepare the first main agent (A1). Separately, the first curing agent (B1) is prepared by mixing the first polyisocyanate compound (b11) and the first organic solvent (b21) having no hydroxyl group.

The obtained first main agent (A1) and first curing agent (B1) are mixed to prepare a water-based primer surfacer (X). Mixing of the first main agent (A1) and the first curing agent (B1) is performed immediately before coating. After being mixed, the first main agent (A1) and the first curing agent (B1) may be supplied to the coating apparatus, or may be mixed within the coating apparatus. The mixing method is as described above.

In the first main agent (A1) and the first curing agent (B1), the hydroxyl group equivalent of the first hydroxyl group-containing resin (a11) and the isocyanate group equivalent of the first polyisocyanate compound (b11) are equal to isocyanate group equivalent/hydroxy group equivalent. = 1/0.5 to 1/2.

When the aqueous primer surfacer (X) contains an epoxy group-containing silane coupling agent, the epoxy group-containing silane coupling agent is added to at least one of the first main agent (A1) and the first curing agent (B1). The silane coupling agent is added in an amount of 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the total solid content of the first hydroxyl group-containing resin (a11) and the first polyisocyanate compound (b11). be.

(Painting method)
The prepared aqueous primer surfacer (X) is applied onto the substrate. The coating amount of the water-based primer surfacer (X) is not particularly limited, and is appropriately set according to the performance required for the coating film. The water-based primer surfacer (X) is applied, for example, so that the thickness of the undercoating film after curing is 20 μm or more and 100 μm or less.

The method of applying the water-based primer surfacer (X) is not particularly limited. Examples of coating methods include air spray coating, airless spray coating, rotary atomization coating, and curtain coating. These methods may be combined with electrostatic coating. In the case of repair, air spray coating is preferred because local coating is easy. Coating may be performed multiple times.

After the water-based primer surfacer (X) is applied, it is heated to cure the coating. Curing conditions are appropriately set according to the coating amount and composition. Curing is performed, for example, at a temperature of 40° C. or higher and 70° C. or lower for about 30 to 60 minutes. After curing, the basecoat is usually sanded and degreased. Polishing is performed using sandpaper or the like.

When repairing, before applying the water-based primer surfacer (X), if necessary, the target portion of the object to be coated and its surroundings are polished, and unevenness is filled with putty. Subsequently, the part is polished again.

(object to be coated)
The shape of the object to be coated is not particularly limited. The object to be coated may be in the form of a flat plate or may have a three-dimensional shape. The material of the object to be coated is also not particularly limited. Examples of the material of the object to be coated include metal, resin, and glass. Metals include, for example, iron, copper, aluminum, tin, zinc, or alloys thereof.

The metal object to be coated may be surface-treated. Examples of surface treatment include phosphate treatment, chromate treatment, zirconium chemical conversion treatment, and composite oxide treatment. The metal object to be coated may be further coated with an electrodeposition paint after the surface treatment. The electrodeposition paint may be cationic or anionic.

Examples of resins include polypropylene resins, polycarbonate resins, urethane resins, polyester resins, polystyrene resins, ABS resins, vinyl chloride resins, and polyamide resins. The resin-made object to be coated is preferably degreased.

Specific examples of the object to be coated include automobile bodies such as passenger cars, trucks, motorcycles, and buses, or parts thereof.

(II) Step of forming a colored base coating film In this step, the water-based colored base coating composition (Y) is applied onto the base coating film to form a colored base coating film. The application of the water-based colored base coating composition (Y) may be carried out multiple times.

(Method for preparing aqueous colored base coating composition (Y))
The aqueous colored base coating composition (Y) may be of the curing type or of the lacquer type. The aqueous colored base coating composition (Y) further contains a pigment. Pigments include, for example, color pigments and/or luster pigments exemplified for pigment (D).

The curable type water-based colored base coating composition (Y) contains a curable resin (for example, the above main agent (A)) and a curing agent (for example, the above curing agent (B)), and is cured by heating. A film is formed. The curable type aqueous colored base coating composition (Y) may further contain a silane coupling agent (for example, an epoxy group-containing silane coupling agent).

The lacquer-type water-based colored base coating composition (Y) contains water, an organic solvent, and a binder resin dissolved or dispersed therein, and volatilization of the water and the organic solvent forms a cured coating film. The concentration of the binder resin is not particularly limited, and is appropriately set according to the composition and application.

The binder resin is not particularly limited. Examples of binder resins include acrylic resins, amino alkyd resins, alkyd resins, amino resins, isocyanate resins, epoxy resins, vinyl chloride resins, cashew resins, silicone resins, styrene resins, styrenated alkyd resins, cellulose resins (e.g., cellulose nitrate, etc.), urea resins, vinyl resins, phenolic resins, phthalic acid resins, fluororesins, polyester resins, unsaturated polyester resins, and modified resins thereof (e.g., rosin-modified, phenol-modified, epoxy resin-modified, styrene-modified , acrylic modification, urethane modification). These are used singly or in combination of two or more. Examples of organic solvents include naphtha, xylene, toluene, and acetone.

(Painting method)
The method of coating the water-based colored base coating composition (Y) is not particularly limited, and includes the same method as for the water-based primer surfacer (X). The coating amount of the water-based colored base coating composition (Y) is not particularly limited, and, for example, it is applied so that the thickness of the colored base coating film after curing is 10 μm or more and 100 μm or less. After coating, the coating is cured. Curing conditions are appropriately set according to the composition of the aqueous colored base coating composition (Y).

(III) Step of Forming Clear Coating Film In this step, the aqueous clear coating composition (Z) is applied onto the colored base coating film to form a clear coating film.

(Method for preparing aqueous clear coating composition (Z))
The second hydroxyl group-containing resin (a12) and the second aqueous solvent (a22) are mixed to prepare the second main agent (A2). Separately, the second curing agent (B2) is prepared by mixing the second polyisocyanate compound (b12) and the second organic solvent (b22) having no hydroxyl group.

The obtained second main agent (A2) and second curing agent (B2) are mixed to prepare an aqueous clear coating composition (Z). Mixing of the second main agent (A2) and the second curing agent (B2) is performed immediately before coating. The second main agent (A2) and the second curing agent (B2) may be supplied to the coating device after being mixed, or may be mixed within the coating device. The mixing method is as described above.

The second main agent (A2) and the second curing agent (B2) are such that the hydroxyl group equivalent of the second hydroxyl group-containing resin (a12) and the isocyanate group equivalent of the second polyisocyanate compound (b12) are equal to isocyanate group equivalent/hydroxy group equivalent. = 1/0.5 to 1/1.5.

When the aqueous clear coating composition (Z) contains an epoxy group-containing silane coupling agent, the epoxy group-containing silane coupling agent is added to at least one of the second main agent (A2) and the second curing agent (B2). . The silane coupling agent is 1.2 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12). added.

(Painting method)
The prepared water-based clear coating composition (Z) is applied onto the water-based colored base coating film. The coating amount of the water-based clear coating composition (Z) is not particularly limited, and is appropriately set according to the performance required for the coating film. The water-based clear coating composition (Z) is applied, for example, so that the thickness of the clear coating film after curing is 20 μm or more and 100 μm or less.

The method of applying the water-based clear coating composition (Z) is not particularly limited, and includes the same method as that for the water-based primer surfacer (X). Among them, air spray coating is preferable. Coating may be performed multiple times.

After the aqueous clear coating composition (Z) is applied, it is heated to cure the coating film. Curing is performed, for example, at a temperature of 40° C. or higher and 100° C. or lower for about 15 to 60 minutes.
In this way, a coated article is obtained which comprises the primer coating, the colored base coating and the clear coating in this order.

EXAMPLES Hereinafter, the present embodiment will be described in more detail using examples, but the present embodiment is not limited by the examples. In the examples, "parts" and "%" are based on mass unless otherwise specified.

[Preparation example]
Based on the formulation shown in Table 1, curing agents HA to HE containing an epoxy group (Ep group)-containing silane coupling agent, comparative curing agent Ha not containing an epoxy group-containing silane coupling agent, amino groups instead of epoxy groups A comparative curing agent Hb was prepared containing a silane coupling agent with The storage stability of the obtained curing agent was evaluated by the following method. Table 1 shows the evaluation results.

Each component shown in Table 1 is as follows.
Polyisocyanate compound A: Barnock DNW-5500 (manufactured by DIC)
Polyisocyanate compound B: Bayhydur ultra 304 (manufactured by Sumika Covestro)
Silane coupling agent A: 3-glycydoxypropyltrimethoxysilane Silane coupling agent B: 3-glycydoxypropyltriethoxysilane Silane coupling agent C: N-phenyl-3-aminopropyltrimethoxysilane

(1) Evaluation of storage stability (1-1) Thickening property The liquid temperature of the sample (curing agent) was adjusted to 23°C. Next, a viscosity cup NK-2 manufactured by Anest Iwata Co., Ltd. was submerged in this sample and pulled up. The time from the moment the sample was pulled up until the sample was completely discharged was measured. This is the initial value T ₀ (seconds).

The sample was then placed in a metal container and sealed. This metal container was stored in a constant temperature room at 50° C. for 30 days. After that, the metal container was taken out from the thermostatic chamber and the liquid temperature was adjusted to 23°C. Subsequently, the time (T (seconds)) from pulling up to discharging the sample was measured in the same manner as described above. TT ₀ was calculated and evaluated according to the following criteria.

Best: TT ₀ within 1 second Good: TT ₀ over 1 second and within 5 seconds Acceptable: TT ₀ over 5 seconds within 10 seconds Poor: TT ₀ over 10 seconds

(1-2) Hue A sample was placed in a metal container and sealed. This metal container was stored in a constant temperature room at 50° C. for 30 days. After that, the metal container was taken out from the thermostatic chamber, and the sample was placed in a test tube and tightly sealed while taking care not to introduce air bubbles. A sample and a Gardner color number standard were aligned and viewed side-through under diffuse daylight for evaluation. If the color of the sample matched, the color number of the Gardner color standard was recorded. If the sample color was between two Gardner color standards, the Gardner color number closest to the sample was recorded. Judgment criteria are as follows.

Best: Gardner color number is 1
Acceptable: 2 to 3 Gardner colors Impossible: 4 or more Gardner colors

Although curing agents HA to HE contained epoxy group-containing silane coupling agents, the storage stability was as good as curing agent Ha containing no silane coupling agent. On the other hand, the comparative curing agent Hb containing a silane coupling agent having an amino group instead of an epoxy group is inferior in storage stability.

In the above preparation examples, various silane coupling agents were added to the curing agent (B) for evaluation. The effect of the ring agent on storage stability is considered to be small.

[Example 1]
A water-based primer surfacer (X), a water-based colored base coating composition (Y) and a water-based clear coating composition (Z) were prepared in the following manner to produce coated articles.

(1) Preparation of water-based primer surfacer (X) As the first main agent (A1) containing the pigment (D), nax E-CUBE WB Plasaf Vita Gray (manufactured by Nippon Paint Co., Ltd., solid content: about 56%) was prepared. The first main agent (A1) contains acrylic polyol in the form of an emulsion as the hydroxyl group-containing resin (a11), and contains pure water as the aqueous solvent (a21). The solid content concentration of the hydroxyl group-containing resin (a11) is 24.4% of the total solid content contained in the first main agent (A1).
As the first curing agent (B1), the curing agent HA prepared above was prepared.
Pure water was prepared as the diluent component (C).

A primer surfacer was prepared by mixing 100 parts of the first main agent (A1), 12.5 parts of the curing agent HA, and an appropriate amount of the diluent component (C) using a disper. The content of the silane coupling agent was 1.18 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a11) and the polyisocyanate compound (b11).

(2) Preparation of water-based colored base coating composition (Y) nax E-CUBE WB412 Silent Black (manufactured by Nippon Paint Co., Ltd., solid content about 22%) 100 parts, nax E-CUBE WB 911 S-binder (auxiliary agent, Japan A lacquer-type base coat paint was prepared by mixing 50 parts of Nax E-CUBE WB R20 standard diluent (diluent component, manufactured by Nippon Paint Co., Ltd.).

(3) Preparation of water-based clear coating composition (Z) As the second main agent (A2), nax E-CUBE WB (2:1) NN clear (manufactured by Nippon Paint Co., Ltd., solid content concentration: about 38%), and pure water (aqueous solvent (a22)) was prepared. The hydroxyl group-containing resin (a12) exists in the form of an emulsion in the mixture. The solid content concentration of the hydroxyl group-containing resin (a12) was 91.5% of the total solid content contained in the second main agent (A2).

As the second curing agent (B2), the curing agent HA prepared above was prepared.
Pure water was prepared as the diluent component (C).

100 parts of the second main agent (A2), 50 parts of the curing agent HA, and an appropriate amount of the diluent component (C) were mixed using a disper to prepare an aqueous clear coating composition (Z). The content of the silane coupling agent was 1.35 parts by mass with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a12) and the polyisocyanate compound (b12).

(III) Preparation of coated article (III-1) Formation of undercoat film A 60 cm × 40 cm steel plate (object to be coated) is coated with a water-based primer surfacer (X) with an air spray gun, and the paint adheres by touching with a finger. Air blow drying was carried out until it disappeared. This coating and drying was repeated two more times. Subsequently, this steel plate was heated in an oven set at 60° C. for 30 minutes to form a base coating film (cured film thickness: 45 μm). Then, the surface of the resulting coating film was polished. Finally, the surface of the coating film was degreased.

(III-2) Formation of water-based base coating film The water-based colored base coating composition (Y) is applied with an air spray gun to an object to be coated having a base coating film, and air blow drying is performed until the paint no longer adheres when touched with a finger. did This coating and drying was repeated two more times to form a water-based pigmented base coating (cured film thickness: 20 μm).

(III-3) Formation of Clear Coating Film The water-based clear coating composition (Z) was applied three times using an air spray gun to the object to be coated comprising the primer coating film and the colored base coating film. Each coat was separated by 1 minute. After that, the object to be coated was allowed to stand for 15 minutes in an environment with a temperature of 23±2° C. and a humidity of 50±2 RH%. Next, the coated article was heated in an oven set at 70° C. for 20 minutes to form a clear coating film (cured film thickness: 50 μm).

[Examples 2-8, Comparative Examples 1-2]
A water-based primer surfacer (X) and a water-based clear coating composition were prepared in the same manner as in Example 1, except that the types of the first curing agent (B1) and the second curing agent (B2) were changed as shown in Table 2. (Z) was prepared to produce a coated article.

[Evaluation method]
The coated articles were evaluated by the following methods. Table 2 shows the evaluation results. The content of the silane coupling agent in Table 2 is the compounding amount per 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a11) and the polyisocyanate compound (b11).
(2) Coating performance (2-1) Adhesion In the cured clear coating, cuts reaching the steel plate (11 vertical, 11 horizontal, 2 mm intervals) were made with an NT cutter (manufactured by NT Corporation), Made 100 squares. A tape (CELLOTAPE (registered trademark), 24 mm width, manufactured by Nichiban Co., Ltd.) was affixed so as to cover all the squares, and was tightly adhered from above with a nail or the like. The tape was then peeled off while being pulled at an angle of about 45° with the coating film. The coating film after tape peeling was visually evaluated. Evaluation criteria are as follows.

10 points: Each cut is fine, both sides are smooth, and no peeling is observed at the intersections of the cuts and in the grids. 8 points: There is slight peeling at the intersections of the cuts, but the grids are No peeling is seen inside, and the area of peeling is less than 5% of the area of the whole square. Less than 15% 4 points: The peeling width in the grid is wide, and the peeling area is 15% or more and less than 35% of the total grid area 2 points: The peeling width in the grid is wider, and the peeling area is the entire grid 35% or more and less than 65% of the square area 0 points: The area of peeling is 65% or more of the total square square area

(2-2) Water resistance 1 (adhesion evaluation after water immersion test)
A constant temperature water bath with circulation was set at 40° C. and filled with deionized water. About 3/4 of the coated article was immersed here. After soaking for 240 hours, the coated article was lifted and lightly wiped to remove water droplets. After being pulled out, the coated article was left at room temperature (23° C.) for 24 hours and evaluated in the same manner as in the above adhesion evaluation (2-1).

(2-3) Water resistance 2 (blister evaluation after water immersion test)
A constant temperature water bath with circulation was set at 40° C. and filled with deionized water. About 3/4 of the coated article was immersed here. After soaking for 240 hours, the coated article was lifted and lightly wiped to remove water droplets. After withdrawal, the coated article was allowed to stand at room temperature (23° C.) for 1 hour and the coating was visually evaluated. Evaluation criteria are as follows.
Best: No abnormalities Good: Very small blisters occur, but there is no practical problem Acceptable: Partial blisters of 1 mm or more Poor: Overall blisters of 1 mm or more

ADVANTAGE OF THE INVENTION According to this invention, the water-based coating composition from which the coating film excellent in water resistance is obtained is provided. Therefore, the water-based coating composition is suitable for coating of automobiles, especially coating for automobile repair.

Claims (8)

a main agent (A) containing a hydroxyl-containing resin (a1) and an aqueous solvent (a2);
and a curing agent (B) containing a polyisocyanate compound (b1) and an organic solvent (b2) having no hydroxyl group,
At least one of the main agent (A) and the curing agent (B) further contains a silane coupling agent having one or more epoxy groups. The content of the silane coupling agent is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1). 1. The water-based coating composition according to 1. A water-based coating composition used as a primer surfacer,
The content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1). 1. The water-based coating composition according to 1. An aqueous coating composition for forming a clear coating film,
The content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the total solid content of the hydroxyl group-containing resin (a1) and the polyisocyanate compound (b1). The aqueous coating composition according to claim 1. A step (I) of applying a water-based primer surfacer (X) to an object to be coated to form a base coating film;
A step (II) of applying an aqueous colored base coating composition (Y) onto the undercoating film to form a colored base coating film;
A step (III) of coating the aqueous clear coating composition (Z) on the colored base coating to form a clear coating,
At least one of the water-based primer surfacer (X) and the water-based clear coating composition (Z) contains a silane coupling agent having one or more epoxy groups. The aqueous primer surfacer (X) comprises a first main agent (A1) containing a first hydroxyl group-containing resin (a11) and a first aqueous solvent (a21);
and a first curing agent (B1) containing a first polyisocyanate compound (b11) and a first organic solvent (b21) having no hydroxyl group,
The silane coupling agent is contained in at least one of the first main agent (A1) and the first curing agent (B1),
The content of the silane coupling agent is 1 part by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the total solid content of the first hydroxyl-containing resin (a11) and the first polyisocyanate compound (b11). A method for manufacturing a coated article according to claim 5. The aqueous clear coating composition (Z) comprises a second main agent (A2) containing a second hydroxyl group-containing resin (a12) and a second aqueous solvent (a22),
and a second curing agent (B2) containing a second polyisocyanate compound (b12) and a second organic solvent (b22) having no hydroxyl group,
The silane coupling agent is contained in at least one of the second main agent (A2) and the second curing agent (B2),
The content of the silane coupling agent is 1.2 parts by mass or more and 10 parts by mass with respect to 100 parts by mass of the total solid content of the second hydroxyl group-containing resin (a12) and the second polyisocyanate compound (b12). 6. A method for producing a coated article according to claim 5, comprising: The method for producing a coated article according to any one of claims 5 to 7, wherein both the water-based primer surfacer (X) and the water-based clear coating composition (Z) contain the silane coupling agent.